Infographic: ElectricityA visual cheat sheet about electrical physics, containing the most important formulas of current and Ohm’s law expressed through an impossible water circuit analogy. (by Pierluigi Scotolati)
It is great for testing real current consumed by electrical gadgets used in our homes. A clamp meter is like a digital multimeter with a jaw which can clamped around a wire of an operating electrical instrument to measure current.
The Physics of the Plasma Universe by Anthony Peratt describes magma as a plasma, a medium containing moving charges. So we should expect volcanoes not only to exhibit electrical behavior but to have that behavior connected with the larger plasma environment, that is, to be elements in a larger electrical circuit.